Evening Emm
I think it depends on the type you buy and where you get them from.
When I'm here on my own in the UK with seriously limited cooking utensils and pans (mum has 2 very small pans and 1 wooden spoon!) I do tend to buy instant meals. Usually not the ping variety though. I get the pre-prepared raw stuff from M&S or Sainsburys, say chicken wrapped in bacon or salmon in white sauce, that you just whack in the oven and I then just have to cook loads of veg to go with it.
I find them convenient and actually very tasty, so yes worth buying and not a waste of money.
Not cheap though I admit when you compare them to what the ingredients would cost.
Mind you I do love Tesco instant chicken and bacon pasta bake. You just stuff it in the microwave for about 7 minutes.
It has low salt, no sugar and no nasty additives and is very tasty and filling and just needs a small salad to go with it.
I have all the time in the world at home and always cook from scratch, but if you are really knackered after a long day at work I can see why busy mum's go for them.